CA1182688A

CA1182688A - Continuous vapor processing system

Info

Publication number: CA1182688A
Application number: CA000405662A
Authority: CA
Inventors: Donald J. Spigarelli; Paul C. Dustin
Original assignee: HTC Corp
Current assignee: HTC Corp
Priority date: 1981-06-23
Filing date: 1982-06-22
Publication date: 1985-02-19
Also published as: DE3223471A1; JPS586774A; US4389797A; GB2105208B; FR2507918A1; FR2507918B1; GB2105208A

Abstract

A B S T R A C T

A continuous vapor processing system for vapor phase soldering, degreasing, or similar processes wherein a product is moved into and out of a vessel in a continuous manner via open conduits or channels while preventing escape of vaporfrom the processing tank and the conduits.

Description

FIELD OF THE INYENTION
__ This invention relates to vapor phase soldering, degreasing, and like systems

2 and, more particularly, to continuous systems open to the atmosphere and having

3 apparatus for conservation and emission control of process vaporO

BACKGROUND OF THE INVE:NTION

4 ;~ Vapor phase systems are known in whi~h a processing vapor is contained in a S vesæel and into which a product is introduced to accomplish a particular process or 6 ~ operation. One sueh system is for vapor phase soldering wherein soïder on a 7 workpiece is caused to melt or reflow by the heat from a condensing heated vapor.
8 ln such a vapor phase soldering system, a fluorocarbon liquid is typically provided 9 in a tank and is heated to a temperature sufficient to produce a hot saturated la vapor above the surface of the liquid and in equilibrium therewith. This liyuid 11 I preferably is a nonconducting chemically stable inert liquid having an atmospheric 12 boiling point at least equal to the soldering temper~ture and which provides 13 non-oxidizing, non-flammable vapor. The tank is usually open to the atmosphere 14 to facilitate product entry and removal, and the vapor can emanate from the open tanlc into the atrnosphere. The release of process vapor into the atmosphere can16 present a health risk, and the magnitude of such emissions are becoming the 17 subject of increasingly stringent governmental and industry health and safety 18 standards. Moreover, the liquid providing the vapor is relatively ea~pensive, and 19 thus for economy of system operation, loss of the liquid through vapor emission into the atmosphere should also be minimized.

6~

One technique for minimizing vapor loss is shown in United States Patent 2 3,904,102 wherein a secondary vapor blanket is provided over the primary or 3 processing vapor to shield the primary vapor from the atmosphere. The secondary 4 vapor blanket is most typically formed of Freon TF (R-113) which stratifies ~bove the primary vapor by virtue of a lower boiling point and a lower density than the 6 primary vapor. Such a dual vapor system presents several disadvantages. The 7 system is inherently more complex than single vapor systems by reason of the 8 addi~ionsl cooling and recovery equiprnent required for the secondary fluid. The 9 secondary vapor is not in contact with its own boiling phase but rather is exposed to the higher temperature primary vapor; thus, the second vapor is caused to exist 11 ~ at a superheated temperature, usually about 180-225 F., which causes breakdown 12 of the matarial into components which can be toxic and corrosive. Acid 13 contaminants can form in the secondary vapor, which can affect the processing d~ systam and add to the cost of its maintenance. The presence of acid contaminants ~ in the secondary vapor can also result in contamination of the product entering and lG leaving the system by way of the secondary vapor blanket. Such acid eontaminants 17 exist in the secondary vapor to some degree even when employing acid removal 18 ~ procedures on the condensed secondary liquid. Moreover, the boiling phase of the 19 prim~ry liquid can g~enerate pollutants such as perfluoroisobutylene (PFIB) whi~h ~' can enter the atmosphere.
21 Systems have been proposed using tank covers to contain the processing 22 vapor, however, vapor loss still occurs when the cover is opened to admit product 23 ~ entry and removaL An improved system for minimizing the problems of vapor loss 24 is shown in United States Patent 4,077,467 of one of the same inventors and the same assignee as herein. In the system therein described, the primary and 26 secondary liquids are separated and contained within closed individually controlled 27 vapor-lock chambers. The separate chambers prevent the vapors from communi-d. h~.,~

cating with each other, inhibit the flow of contaminants, minimize vapor loss ~nd 2 avoid fluid breakdown due to ex~essive heating. The separation OI the chambers is 3 achieved by movable doors which sequentially open to admit the work and close 4 behind the work; Rfter the soldering is completed, the doors operate in reverse sequence. However, this added equipment co nplexity somewhat hampers the vapor 6 phase soldering operations in an autonnated manufRcturing facility. Furthermore, 7 to a lesser extent, some of the above-rnentioned vapor loss problems persist.
8 A system showing the continuous passage of articles into and out of the 9 vessel containlng the vapor is shown in United States Patent 3,866~307, wherein the process vessel includes an inlet conduit and an exit conduit, each dispo~ed at the 11 tol? of the vessel above the vapor zone, and each having cooling coils which assist 12 . in retaining the vapor within the vessel. Articles to be processed are conveyed in a 13 curved path downward from the inlet conduit into the vapor and upward from the 14 vapor to the outlet conduit. This apparatus has application to manufa~turing 15 ,, processes, generally limited to where the vapor entry and exit and ~urved path are 16 permissible. Vapor loss can al90 occur from the rela~ively large inlet and outlet 17 ports.
, According to the present invention there is provided a continuous vapor phase processing system compris-r 1 ing a vessel containing a processing vapor in a vapor zone a first aperture. ~n the vessel side wall within the vapor zone and by which a work product is lntroduced into the vapor zone, and a second aperture in the confronting vessel side wall within the vapor zone and by which a work product is removed from the vapor zone; a first conduit in commun-~1 ication with the irst aperture and extending outwardly 22 from the vessel and having an outer end open to the atmosphere;
23 a second conduit in communicati.on with the second aperture and outwardly extending from the vessel and having an outer end open to the atmosphere; each of said condults having a preselected cross-section and length selected to just allow passage of a work product therethrough while providing an intended flow resistance to the processing vapor to prevenk significant vapor flow along the conduits; cooling means associated with each conduit for cooling the processing vapor to below its condensation temperature to prevent significant vapor loss rom the outer end of the conduit to the atmosphere; means for conveying a work product through said first conduit into the vapor zone of said vessel and out of the vessel through said second conduit;
and said conduits being substantially in alignment on respective sides of the vapor zone to provide substantially straight-through conveyance of a work product through the first conduit into the vapor zone of the vessel and out of the vessel through the second conduit.
In embodiments of the invention, a productcan be moved into ~nd out of the vess~l in a continuous manner bv way o:~ the open ~onduits, typically by means of conveyors disposed within the eonduits and within the vessel to aceomplish product transport into and oul: of the processing zone. A single vapor system can be provided or a dualvaporsystem where~ a second~y vaporisprovidedabovetheprimary vapor zone to prevent loss of the primary vapor frorn an open vessel top. A secondary 20 v~por zone can aLso be created within the conduits to isolate the primhry vapor from the open conduit ends. A horizontal orientation of the open conduits is usually preferred to permit linear conveyance of work through the processing system. The conduits c~n also be inclined either upward or downward to suit intended product transport paths. Upward incline of the conduits also aids in Yapor 2 5 retention of' the heavier-than-air vapor.

~ mbodlments of the inver.tion will now be described, by way of example, with reference to the accompanylng drawings in which:-Fig. l is a selectional elevation view of anembodiment of a continuous vapor processing system according to the invention.

Z6~

Fig. 2 is A top view of the system of Fig. 1;
2 Fig. 3 is a pictol~iRl view, partly cutaway and in section, of a conduit of the 3 system of Figs. 1 and 2;
4 Fig. 4 is ~ cutaway sectional elevation view of an embodiment of the invention having a downward slopir4~ conduit and condensed vapor recovery 6 apparatus; and 7 . Fig. S is a cut~way sectional elevation view of an embodiment Q~ the 8 inYention having an upwardly inclined conduit and a secondary vapor in th~ vessel 9 and conduit.

,, Referring to Fig. 1, there is shown a closed vessel 10 having apertures 12 11 1, snd 14 at the sides, by which the work 26 is introduced into ~nd removed from the 12 I vessel for proeessing therein. The vessel lû contains ~ liquid 16 which is heated by 13 . heaters 18 to produee a vapor within the vessel. The vapor is cooled by cc~l-14 ~ ing coils 22 which cause the vapor to remain in a controlled vapor zone 20 throuc ; which the w~rk will pass. Conduits 28 and 30 each extend horizontally outward ~rc 16 ~ vessel 10 and are in communication with respective apertures 12 and 14~ The 17 conduits include conveyors 32 and 34, respectively, and work is transported by 18 conveyor 32 into the vapor zone, by conveyor 24 through the zone, and by 19 conveyor 34 from the vapor ~one.
A cooling coil 36 is disposed around aperture 12, and a cooling coil 38 is 21 disposed around aperture 14 to minimize the amount OI vapor entering the 22 respective conduits 28 and 3~. Cooling coils 40 and ~2 are provided along the 23 Iength of respective conduits 28 and 30, and are operative to condense the vapor that flows from the vapor zone in vessel 10 into the conduit channels and prevent 2 vapor loss from the channels to the atmosphere. The cooling coils 40 and 42 can 3 extend along the full length of the respective conduits, or a portion thereof, 4 depending upon the degree OI cooling necessary in specific apparatus to achieve vapor condensation. The channels are relatively long and of small cross section to 6 impede vapor flow. The apertures 12 and 14 and the channels within conduits 28 7 and 30 are of cross-section which is as small as practical for transport of work 8 therethrough while minimizing the amount of vapor flow. The cooling coils 36 and 9 38 cause preferential condensation thereon, thereby reducing vapor flow into the conduits, and the cooling coils 40 and 42 are operative to cool and condense the11 vapor that does enter the conduit channels, to prevent escape of any appreciable 12 amount of vapor from the outer ends of the conduits. In the illustrated 13 embodiment having horizontal conduits, the bottom walt of each conduit can be 14 downwardly sloped toward the vessel to permit gravity flow of condensed vapor in 15 ! the conduits baclc into the vessel to be reheated and revaporized. It will be 16 appreciated that work 26 can be continuously processed through the vessel at a 17 rate determined by the speed of the conveyors 32, 249 and 34.
18 The conveyors are more particularly illustrated in Fig. 20 The conveyor 24 19 within the vessel 10 eomprises three parallel conveyor belts 24a, 24b, and 24c which are disposed in parallel spaced relationship within the vessel and are movable 21 about shafts 2S and 27. The conveyor 32 comprises a pair of belts 32n and 32b 22 which are disposed within the spaces provided by the spaced belts 24. The23 belts 32a and 32b are movable on shaft 25 and a shaft 31 (Fig. 1~ disposed at the 24 outer end of conduit 28. The conveyor 34 also comprises a pair of belts 34a and 34b which are disposed within the spaces between belts 24 and movable about 26 shaft 27 and a shaft 29 (Fig. 1) provided at the outer end of conduit 30. The 27 conveyor belts are operated in unison by a drive mechanism (not shown) to ~ ~26~

transport the work 26 in a path through conduit 28, the vapor zone of vessel 10, and 2 conduit 30. The conveyor speed can be controlled such that the work is present 3 within the vapor zone for a time suitable to the particular process being performed 4 therein.
s The construction of ~he conduil and the disposition of the conveyors therein 6 is illustrated in Fig. 3. For purposes of discussion, the conduit 30 is shown, it being 7 understood that the conduit 28 is of the same construction. The conduit 30 8 includes a generally rectangular channel 44 formed by top wall 46 and bottom 9 wall 48. The channel is configured to accommodate the product 26 transported therethrough. In the illustrated ernbodiment, the channel is a narrow slit to accept 11 a thin sheet product such as printed circuit boards. A pair of recessed channels sn 12 and 52 are provided in bottom wall 48 to accornmodate the respective eonveyor 13 belts 34a and 34b. Each conveyor channel includes a bottom floor 54 and an 14 intermediate floor 56 on which the respective courses of the associated conveyor belt are disposed for travel within the channeL The channels are sufficiently deep 16 ' to permit the respective conveyor beïts to be retained at or just below the surface 17 of wall 48 The conveyor belts themselves are of known construction and comprise 18 1 a plurallty of substantiaily identicsl wire link elements 58 which are interlockin~
19 and pivotable about adjaeent links. The belts include raised link portions 60 at 20 l regularly spaced intervals along the belt and which serve as supports on which the 21 work 26 rests. The work is thus supported at spaced points off the surfaces of the 22 conduit channels. Alternatively, the raised link portions can be arranged to engage 23 confronting edges of the work product 26 to propel the work through the entrance 24 channel and restrain work against sliding in the exit channeL
The spaced belts 34 are driven on a common shaft with the spaced belts 24 26 which, in turn, are driYen on a common shaft with the spaced belts 3S~. The 27 belts 24 move about a closed loop path disposed wholly within the vapor processing ., 61~

zone of the vessel 10. The belts 24 thus remain at a uniform temperature present2 within the vapor zone and also remain exposed to the controlled atmosphere within 3 the vesseL The conveyors 32 and 34 are within the relatively cooler environment 4 of the respective conduits and do not materially affect the temperature control of the processing vapor within the vessel.
6 The embodiment of Figs. 1-3 in a typical implementation for the processing 7 of printed circuit boards or other similar thin sheet-like products, has a narrow 8 rectangular channel in each conduit which is about 181/2 inches wide and about 9 1/4 to 1/2 inch in height. In the absence of the cooling coils 36 and 38 at the entrance apertures of the respective conduits9 the fluid dynamics for the dimen-11 j sions set forth will result in vapor loss from the vessel into each conduit of about 12 3 percent for a 1/4 inch channel height, and about S percent for a 1/2 inch channel 13 height. The cooling coils 36 and 38 are significantly cooler than that of the vapor1 14 l and the vapor is caused to preferentially condense on the coils 38 and 38, as a lS 'i resuit of which vapor loss into the conduits is reduced from the percent~ges given 16 i, above. The coils 36 and 38 are maintained at a temperature to provide the 17 I preferential condensation without substantial effect on the temperature of the 18 I heated processing vapor. The relatively small amount of vapor which does flow 19 j from the processing zone into the conduits is condense~ within the condui$s by 2n ' action of the cooling coils disposed along the conduit such that no significant Yapor 21 ~ loss occurs from the open outer ends of the conduits. The lerlgth of the conduits is 22 determined to provide the intended flow resistance to impede outw~rd flow of 23 vapor along the conduit, and to allow sufficient cooling of vapor along the conduit 24 length. A conduit length of 4 to 6 feet is typicaL In some instances, forced cooling along the conduit may not be neCeSSLry to minimize the escape of vapor 26 from the conduit end. The length can be sufficient to minimize such escape by 27 natural cooling along the conduit and the inhibition of flow by the conduit length 28 and cross-section.

g _ 6~3 While the embodiment described ~bove employs conduits which are hori 2 zontal, the invention may also be implemented by conduits which are inclined 3 upward or downward from the vesseL Moreover, the invention can be employed in 4 dual vapor systems as well as in single vapor systems, such as when the aspect ratio of the conduit channels does not allow full vapor controL
6 An alternative embodiment is shown in Fig. ~ wherein a conduit 62 is shown 7 downwardly disposed from vessel lQ. The vapor 20 is more dense than air ~nd the downward slope of the conduit will increase the tendency of outward vapor flow g and escape from ~he conduit end. By virtue OI the invention, however, vapor loss is minimized to prevent any appr~iable escape from the conduit. Cooling coils 64 11 are disposed around the conduit along the length thereof. A sump 66 is provided in 12 the botSom of the conduit at a position outward from the vessel, and a return 13 pipe 68 connects the sump 66 with ~he vessel 10 to permit condensed vapor to be 14 returned to the vessel for reheating and revaporization. In operation9 vapor which enters the conduit via aperture 14 is cooled and condensed by cooling me~ns 64, 16 ~ and the cond~nsing ~iquid is colle~ted in sump 66 for return to the vesseL The 17 coo~ing action LS controlled to achieve ~ondensation of substantially all vapor in the ~LR ~onduit su~h that no appre~iable vapor escapes from the outer conduit end.
A further embodiment is shown in Fig. 5 as adapted to a dual vapor ~y~tem. The vessel 10 includes a first vapor within a processing vapor zone 20 as described abo~e, and a second vapor within a secondary vapor zone 70 dlsposed above the primary vapor. Cooling coils 72 cool the secondary vapor and rnaint~in this secondary vapor within a defined zone above the prim~ry vapor æone, with a boundary or interface9 illustrated by reference 74, existing between the two vapor zones. Secondary v~por condensed by action of thecooling coil 72 is collected by a trough 76 and directed by a pipe 78 to a reservoir 80. The conduit 82 in this embodiment extends upwardly from the vesseland includes a sump 84 with an outlet pipe 86 for returning condensed secondary v2por to the reservolr 80. Prirnary cooling coils 86 are disposed along a portion of 2 conduit 82, and cooling coils 88 are disposed around the conduit 82 at a position 3 outward of the primary coils 86 ~nd at the height of the secondary zone 70. Spray 4 nozzles 90 are disposed within the conduit at Q position outward from the cooling coils 88, these nozzles being fed by a pump 92 supplied by condensate from 6 reservoir 8 0.
7 Primary vapor entering the conduit 82 from the primary vapor zone of the 3 ves~el is condensed by cooling coils 86, the condensing vapor flowing bflck into the 9 vessel. Secondary vapor condensate collected in reservoir 80 is applied as a fine spray or mist by nozzies 90 which are directed inwardly of the conduit 82. This 11 mist serve~ as a liquid seal to further contain the vapor within the conduit. The 12 spray seal can also be employed in the embodiments described above.
13 The ~d~ts thus described are operative to m~niln~ze to a substantlal 14 degre~ the loss OI vapor from the processlng systean while maintaining ~n open ~ system for continuous throughput of a produ~ t to be processed within the vesseL
16 The vapor loss from the open conduits can be less than the loss which occurs in ; convention~l dual vapor systems. Moreover, the sm~ll vapor loss of the novel 18 I system does not vary to any appreci~ble extent with the inclination of the conduits 19 in reiation to the vesseL In embodiments where the conduits are inclined, an inclin~.ion in the range of 5-10 Irom the horizontal is typicQL The entrance 21 conduit and exit conduit can each be disposed in an upward inclination, Q downward 22 inclination, or horizontal disposition, and the disposition of each conduit need not 23 be the same as the other. Accordingly, the invention is not to be limited by what 24 has been particularly shown and described except as indicated in the appended claims.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. A continuous vapor phase processing system comprising:
a vessel containing a processing vapor in a vapor zone, a first aperture in the vessel side wall within the vapor zone and by which a work product is introduced into the vapor zone, and a second aperture in the confronting vessel side wall within the vapor zone and by which a work product is removed from the vapor zone;
a first conduit in communication with the first aperture and extending outwardly from the vessel and having an outer end open to the atmosphere;
a second conduit in communication with the second aperture and outwardly extending from the vessel and having an outer end open to the atmosphere;
each of said conduits having a preselected cross-section and length selected to just allow passage of a work product therethrough while providing an intended flow resistance to the processing vapor to prevent significant vapor flow along the conduits;
cooling means associated with each conduit for cooling the processing vapor to below its condensation temperature to prevent significant vapor loss from the outer end of the conduit to the atmosphere;
means for conveying a work product through said first conduit into the vapor zone of said vessel and out of the vessel through said second conduit; and said conduits being substantially in alignment on respective sides of the vapor zone to provide substantially straight through conveyance of a work product through the first conduit into the vapor zone of the vessel and out of the vessel through the second conduit.

2. The system of claim 1 wherein said cooling means includes cooling means at each of the apertures to cause condensation of vapor thereon and minimize the flow of vapor from the vessel into the conduits.

3. The system of claim 1 wherein said cooling means includes cooling means along each conduit to cause condensation of vapor therein and prevention of significant vapor loss from the outer ends of the conduits to the atmosphere.

4. A continuous vapor phase processing system comprising:
a vessel containing a processing vapor in a vapor zone, a first aperture in the vessel side wall within the vapor zone and by which a work product is introduced into the vapor zone, and a second aperture in the confronting vessel side wall within the vapor zone and by which a work product is removed from the vapor zone;
a first conduit in communication with the first aperture and outwardly extending from the vessel and having an outer end open to the atmosphere;
a second conduit in communication with the second aperture and outwardly extending from the vessel and having an outer end open to the atmosphere;
first cooling means at each of said apertures for condensation of vapor to minimize the flow of vapor from the vessel into the conduit;
each of said conduits having second cooling means for condensation of vapor in the conduit which has entered from the vessel, to prevent significant vapor loss from the outer end of the conduit to the atmosphere; and means for conveying a work product through said first conduit into the vapor zone of said vessel and out of the vessel through said second conduit; and said conduits being substantially in alignment on respective sides of the vapor zone to provide substantially straight-through conveyance of a work product through the first conduit into the vapor zone of the vessel and out of the vessel through the second conduit.

5. A continuous vapor phase processing system comprising:
a vessel containing a primary, processing vapor in a processing vapor zone and a second vapor in a secondary vapor zone above the processing vapor zone;
a first conduit outwardly extending from the vessel side wall and having an inner end in communication with the processing vapor zone and an outer end open to the atmosphere;
a second conduit outwardly extending from the confronting vessel side wall and having an inner end in communication with the processing vapor zone and an outer end open to the atmosphere;
each of the conduits having first cooling means for providing condensation of primary vapor to minimize primary vapor flow along the conduit, and second cooling means outward of the first cooling means for providing condensation of secondary vapor to prevent significant loss of vapors from the outer end of the conduit to the atmosphere;
means for conveying a work product through said first conduit into the processing vapor zone of said vessel and out of the vessel through said second conduit; and said conduits being substantially in alignment on respective sides of the processing vapor zone to provide substantially straight-through conveyance of a work product through the first conduit into the processing vapor zone of the vessel and out of the vessel through the second conduit.

6. The system of claim 4 or 5 where said first and second conduits are each of configuration selected to just allow passage of work product therethrough while providing an intended flow resistance to the processing vapor to prevent significant vapor flow along the conduits.

7. The system of claim 1, 4 or 5 wherein each of said conduits includes:
a channel extending throughout the length of the conduit between the aperture in the vessel wall and the atmosphere and configured to allow passage of a work product therethrough;
at least one recessed channel in the bottom wall of the conduit to accommodate a conveyor belt; and wherein said conveying means includes a conveyor belt disposed for movement in the recessed channel of the conduit for transport of a work product through the conduit.

8. The system of claim 1, 4 or 5, wherein said conveying means includes:
at least one conveyor belt disposed in the first conduit and operative to transport a work product therethrough into the processing vapor zone of the vessel;
at least one conveyor belt in the processing vapor zone of the vessel and operative to transport a work pro-duct from the first conduit to the second conduit; and at least one conveyor belt disposed in the second conduit and operative to transport a work product from the processing vapor zone through the second conduit.

9. The system of claim 1, 4, or 5 wherein said conveying means includes:
a plurality of spaced parallel conveyor belts disposed in the first conduit and movable in a closed path within the first conduit about first and second shafts at respective ends of the first conduit;
a plurality of spaced parallel conveyor belts disposed in the second conduit and movable in a closed path within the second conduit about third and fourth shafts at respective ends of the second conduit;
a plurality of spaced parallel conveyor belts disposed in the spaces provided by the spaced belts of the first and second conduits and moveable in a closed path about the first and third shafts;
all of said belts being driven in unison to transport the work product in a path through the first conduit, through the processing vapor zone, and through the second conduit.

10. The system of claim 1, 4 or 5 wherein at least one of the first and second conduits is upwardly inclined from the vessel.

11. The system of claim 1 wherein at least one of the first and second conduits is downwardly inclined from the vessel.

12. The system of claim 4 wherein at least one of the first and second conduits is downwardly inclined from the vessel.

13. The system of claim 11 or 12 wherein each downwardly inclined conduit includes a sump in the bottom of the conduit at a position outward from the vessel for collecting condensed vapor therein; and means for returning the condensed vapor from the sump to the vessel.

14. The system of claim 5 including means for providing a spray of secondary liquid near the outer end of at least one conduit to provide a liquid seal in the conduit for containment of vapors therein.

15. The system of claim 5 including means for collecting condensed secondary vapor in each conduit for return to the vessel.

16. The system of claim 5 including cooling means at the inner end of each said conduits for condensation of vapor in the processing vapor zone to minimize the flow of vapor from the vessel into the conduits.